The present invention relates to a tire inflation pressure detecting device for detecting tire inflation pressure of a vehicle and particularly, it relates to a technique for specifying respective positions of the tires.
There has been proposed and practically used a tire inflation pressure detecting device that detects tire inflation pressures of a vehicle at it traveling and provides resulting pressure information to a passenger in the vehicle in real time.
The tire inflation pressure detecting device in an earlier art has pneumatic sensors each arranged in respective tires of the vehicle to detect respective tire inflation pressures, transmitters each arranged in the tires to transmit so-obtained tire inflation pressure data to the outside and a receiver arranged in a vehicle body to receive the tire inflation pressure data. Then, the tire inflation pressure data received by the receiver is displayed on display means to the passenger.
In the tire inflation pressure detecting device, however, it is impossible to identify which of the tires corresponds to the received tire inflation pressure data. In detail, since the receiver is adapted so as to receive the tire inflation pressure data transmitted from the transmitters installed in four tires, if the tire inflation pressure is reduced, it is impossible to recognize which of the four tires is subjected to a reduction in tire inflation pressure.
Under such a situation, Japanese Patent Application Laid-open Nos. 2000-71726 and 11-78447 disclose a method of specifying the position of a tire subjected to a reduction in tire inflation pressure. According to the method, respective identifying codes are established to the transmitters in the tires while storing the identifying codes in a memory (EEPROM) of the receiver. On the establishment, it is carried out to compare the identifying codes involved in the pressure data transmitted from the transmitters with the identifying codes stored in the memory, thereby specifying the tire having a reduced pressure.
In the above conventional method, however, the tire inflation pressure detecting device has a tendency to be a grand production since the receiver has to be equipped with the memory (EEPROM) and the identification codes stored therein must be compared with the identification codes on the transmitters' side. Additionally, since the compliance relationship between the identification codes on the transmitters' side and the identification codes stored in the EEPROM would collapse at a “tire-rotation” where the conventional positions of the tires are modified in view of improving their lives, it is necessary to rewrite the identification codes stored in the EEPROM, requiring lots of labor for rewriting them.
As one method of solving the above problem, there may be expected a two-way radio communication that enables the tires to be specified with no identification code owing to two-way communication between the tires' side and the vehicle's side. Also in this case, however, the tire inflation pressure detecting device would be large sized while causing the manufacturing cost to be elevated.